1. Field of the Invention
The invention relates to methods and apparatus of physical separation of solids from fluids or for mixing fluids. More specifically, the invention relates to methods and apparatus for separating solids from fluids and mixing fluids by using a ring having a plurality of grooves through which fluid passes. The methods and apparatus of the present invention are particularly suitable for use in treatment of aqueous fluids, such as water and wastewater, by dynamic separation of contaminants to be removed and by dynamic mixing of treating agents to be added as part of treatment. The also present invention generally relates to methods and apparatus for increasing suction of fluids by venturi or eductors (sometimes also referred to as “injectors,” “inductors,” or “aspirators”). More specifically, the invention relates to methods and apparatus employing linear venturi extended in a line, to draw large quantities of gases, liquids, or powdered solids by suction into fluids (liquids or gases).
2. Description of Related Art
Commercial and industrial processes currently employ countless operations involving mixing of fluids (liquids with liquids, gases with liquids, and gases with gases) or separation of fluids or solids from other fluids
For example, excessive contaminants must be removed from the wastewater of food service institutions (restaurants, cafeterias, hospitals, etc.) before the water may be discharged. If established discharge-contamination levels are exceeded, cities and other governmental authorities may impose surcharges on the food service institutions. These surcharges increase the costs of doing business.
Typically, food service establishments are required to have grease interceptors, commonly called “grease traps,” installed in wastewater outlets with sampling wells downstream of the grease traps before the discharge enters the public sewage lines so the authorities can check the discharge from each facility. When the grease traps become full, the contaminants collected in them are removed by vacuum trucks and further treated before discharging to the public sewage.
In addition to the problem of discharging excessive contaminants to public sewage systems, animal fat rendered during the cooking process can congeal when mixed with cold water and clog up the drain lines from the kitchens to the grease traps. When this occurs, the businesses may be shutdown and typically require routing out with a rotor cutter driven by a mechanical cable to open the lines.
Some of the contaminants are destroyed in the grease traps by bacteria. When the contaminants exceed the capacity of what the bacteria can consume, they must be removed from the grease traps by vacuum trucks, or they are discharged to the public sewer, which can result in surcharges as mentioned above.
Bacteria are active only at the limited outer surface of the contaminants to be consumed as food. The bacteria produce enzymes to disperse the contaminants and increase the amount of surface, and the amount of food, available to them. A different enzyme may be required to disperse each contaminant present. When the food is available, bacteria can reproduce in large quantities in very short periods of time. Oxygen dissolved in the water drained into grease traps can become quickly depleted, and aerobic bacteria (those requiring oxygen continuously in order to survive) die. This leaves the task of consuming the contaminants to the anaerobic bacteria (those requiring the absence of oxygen in order to survive). Anaerobic bacteria are not as efficient as aerobic bacteria in consuming the contaminants, and they also produce offensive odors in the process of consuming their food. The offensive odors are prevalent around businesses with grease traps.
Feeding aerobic bacteria in the drain lines from the kitchens has been somewhat successful at either keeping the lines from clogging or increasing the intervals between the times mechanical routing is required. As soon as the aerobic bacteria reaches the grease trap with the oxygen depleted, they die.
Attempts have been made to keep the bacteria alive by bubbling air in grease traps with limited success. Bubbling air even with the finest diffusers creates a large amount of foam in the grease traps. Therefore, air injection has been largely limited to short periods of time and to smaller systems.
Air bubbles rise quickly out of the water, and the bottom of the grease traps return to an anaerobic condition almost immediately preventing the efficient aerobic bacteria from consuming the solids on the bottom of the grease trap. This limits the bubbling of air to the upper part of the grease trap. When oxygen reaches the anaerobic bacteria on the bottom of the grease trap, they die. Therefore, a periodic kill of the anaerobic bacteria on the solids settled on the bottom of the grease trap can be expected. When left for an extended period of time, the solids on the bottom of the grease trap can become packed and act as a seal to prevent oxygen from penetrating into the solids. Only floating contaminants are then consumed by the aerobic bacteria. The offensive odors are also not eliminated.
Therefore, in the food service industry, there is a need for an efficient apparatus and method that can effectively remove particles from wastewater without the problems mentioned above, e.g. incurring surcharges for unsuccessfully meeting contaminant levels, producing offensive odors, requiring the introduction of bubbling air, thus increasing costs, etc.
Another industry faced with the problem of removing contaminants from fluids is the vehicle washing industry. Water used for vehicle washing typically contains significant amounts of suspended solids, dissolved minerals, and organic materials, including oils and other hydrocarbons. Detergents and other chemicals used in the wash operation present further difficulties to the discharge problems. The wash water with the contaminants is typically drained into some type of still pool as a pit or sump. Some of the still pools function as settling basins for the suspended solids and as oil interceptors similar to the grease traps used in food processing facilities.
The water is typically reused in the washing part of the wash cycle until it becomes apparent that the quality of the vehicle wash is no longer satisfactory. Vacuum trucks are then used to remove the contaminants from the sumps and haul them away to disposal sites. Still pools are optimal breeding ground for anaerobic bacteria, which give off a strong and unpleasant odor. The offensive odors are often detected by customers, especially early in the morning when the systems have been shutdown for the night. Bubbling large quantities of air in the still pools can reduce the offensive odors.
The bubbling of air continuously can cause a foaming problem in the sumps. In addition to the offensive odors, governmental regulations may limit the amount of contaminants that can be discharged into the public sewer systems and totally prevent discharge to the environments.
Multiple attempts have been made to improve the process of separating particles from fluid. For instance, U.S. Pat. No. 5,647,977 discloses that the water from vehicle wash facilities can be completely recycled, without water discharge. However, where the cost of water is not a factor and the public sewage system can accept certain contaminants, a complete recycling system may not be cost justified. In such systems, aeration by dissolved oxygen can be used to element the foul odors without the foaming problems typically caused by continuously bubbling air in the sumps. Additional treatment to remove the suspended solids and reduce the organic materials in the sump, other than detergents, can render the water suitable for reuse in the washing part of the vehicle wash cycle, or for discharge where permitted in selected public sewage systems.
Another industry faced with the problem of separation of suspended solid particles from fluids is the water treatment industry. Typically, the solid particles are removed by settling in still pools, centrifugal separation by cyclone filters, and adding flocculating accelerators followed by clarification. Secondary filtration of the fluids often follows the bulk removal operations. The solid particles have to be concentrated and dewatered after separation for disposal. These steps may increase the time and money associated with the particle-removal operation.
An industry having the need to aerate water is the livestock industry. Concentrated animal feeding operations including cattle, swine, poultry, sheep, horses, etc. typically have ponds called “lagoons” in which all animal waste is collected. Aeration with dissolved air in water continuously circulating through the lagoons allows naturally occurring bacteria to thrive in the nutrient rich environment of lagoons and greatly accelerate decomposition of the organic waste. Similarly aquatic farms, such as for fish and shrimp, with concentrations of species may require injection of supplementary oxygen in the water to replace oxygen consumed by decaying plants.
To remove contaminants from wastewater, many present applications employ a cyclone filter. A typical cyclone filter is an apparatus that can be used to separate suspended solids from fluids (such as solids from water and air) and to separate fluids of different densities (such as oil and water) by using the centrifugal force caused by a forced spiral vortex. The external force used to generate the spiral vortex in a cyclone filter is typically provided by injecting a stream of a contaminated fluid at high velocity into the filter at one end perpendicular and at a tangent to the cylinder in which the fluid circulation occurs. The axis of circulation in a cyclone filter can be at any angle from vertical to horizontal.
When the axis of circulation is vertical, the direction of the forces of gravity are, therefore, equal around the entire circular path of the fluid. When the axis of circulation is at some angle other than vertical, the design of the cyclone filter has to account for the differences in the direction of the forces of gravity acting on the fluid as it flows while circulating with or against the forces of gravity.
The design of the inlet through which the high velocity fluid is introduced becomes a major factor in the effectiveness of present cyclone filters, especially in the separation of very fine (small) solid particles from fluids.
Present cyclone filters typically have only one inlet through which the fluid and contaminant mixture is introduced. The single inlet may be typically round or rectangular. And in present cyclone filters, the inlet must supply fluid tangentially to the filter. This may lead to difficulties in certain applications.
Several attempts have been made to improve the efficiency and effectiveness of cyclone filters. For instance, U.S. Pat. No. 5,882,530 describes using a cyclone separator in which the lower frustoconical surface contains porous surfaces. The cyclone separator of the '530 patent may be used for separating a suspension. However, it has been found that over time, particles concentrate along the inner walls of the apparatus as a result of centrifugal forces and tend to clump together and adhere to the porous walls. This clump formation or caking impedes the exit of the carrier fluid through the porous walls.
Other attempts include those disclosed in U.S. Pat. Nos. 5,021,165, 5,478,484, and 6,024,874. However, these attempts generally require the incoming fluid to be tangentially fed into cyclone filter. This limits the use of the filters when tangential feeding is not possible, for example.
Thus, a need exists for an improved apparatus and method of removing particles from fluids. It is desirable that the apparatus and method remove particles at a desired level to reduce the chance of the imposition of a surcharge. It is desirable that the method should not increase costs or increase time involved in removing the particles. An apparatus that does not have to input the fluid tangentially is desired. A need also exists for an improved method of mixing fluids or aerating fluids in a timely fashion.
Further, venturis employing Bernoulli's theorem have been used in countless apparatus to produce differential pressures for mixing of fluids with other fluids (gases with gases, gases with liquids, and liquids with liquids) or solids, measurement of flow, and removal of gases by suction (such as in a liquid or a vacuum chamber). The venturi has also been used for the movement of solids by suction. The venturi is a universal technology that has been used for generations in commercial, industrial, municipal, agricultural, military, and other industries. The configuration of the typical venturi in existing apparatus is a round area (or tube) reduced into a smaller round area (the venturi) to increase the velocity of a flowing fluid to create a low pressure that can be used for suction through a gap at the venturi, or reduced area. The suction is generally around the circumference of the reduced area. It is also generally known that the highest velocity of a liquid flowing through a pipe or tube is at the center of the stream. Therefore, the highest velocity flowing through a round venturi is away from the outer circumference, or edge, of the stream where the suction occurs.
Because of this the size of the stream can also affect the efficiency of the venturi, with the larger diameter venturi having a decrease in efficiency. A round or circle configuration has the largest cross sectional flow area to the length of its edge (or border) than any other configuration possible. Restated, this provides a low suction-gap-length-to-flow-volume ratio. The existing round venturi low suction-gap-length-to-volume ratio make them notoriously inefficient at transferring a secondary fluid from outside the venturi to a primary fluid flowing through the inside of the venturi. The inefficiency is the primary reason the venturi has not received wide application in municipal wastewater treatment, the largest potential area of application that desperately needs to increase aeration efficiency because of that size and the associated high costs of energy.
For convenience water is used as the operating or primary fluid to create suction in the venturi, and air as the secondary fluid drawn into the venturi by suctions in the discussion of the present invention. It should be understood, however, that the present invention applies to all fluids (liquids and gases) that will flow under pressure through a venturi as a primary fluid to create suction and any fluid (gas or liquid) or powdered solids that can be drawn into the primary fluid by suction. The present invention overcomes the deficiencies of existing venturi technology by employing linear venturi (as in a narrow ring to form a curved or round venturi opening as the area of flow, or as in an extended straight line to form a narrow rectangular venturi opening as the flow area) to increase the length of the stream of primary fluid in contact with the venturi gap resulting in an increase of secondary fluid drawn into the primary fluid stream. As an example, a typical existing round venturi with a one-inch diameter area has 0.785 square inches of flow area and a 3.1416-inch circumference.
The length of contact with the suction gap is equal to the 3.1416-inch circumference. A one-eighth inch width round venturi ring flow area, or opening, of the present invention with the same area of flow has an average diameter (from the center of the venturi ring opening) of two inches and a circumference length of 6.283 inches. Suction gaps could be on either one side (6.283 inches) or on both sides (12.566 inches) of the venturi ring opening or area of flow. A one-quarter inch width round venturi ring has an average diameter of one inch and a circumference of 3.14 inches, with a suction length of either 3.14, or 6.28 inches if suction were added to both sides of the venturi. A rectangular venturi having the same flow areas with a one-eighth inch opening width could also be 6.283 inches long with suction on either one side (6.283 inches) or on both sides (12.566 inches) of the venturi opening.
The width of the venturi flow area, or opening, may be determined by the size of solid particles in the fluid flowing through the venturi, the viscosity of the fluid, and the allowable pressure-drop of the specific application. The length of the venturi flow area may be determined by the amount of secondary fluid that needed to be drawn into and mixed with the primary fluid in each application. As an example of using a filtered water as the primary fluid and air as the secondary fluid to be drawn into and mixed with the water by suction, a 1/16-inch wide venturi with the same flow area (0.785 in2) has a length of 12.56 inches, and a suction length of 25.12 inches with suction in contact with both sides of the venturi opening. The example is not intended to limit the venturi width, length, area of flow, and amount of flow (flowrate) of the present invention. Any size venturi can be selected for any amount of primary fluid and secondary fluid flowrates needed in specific applications. The present invention allows the operation of the venturi at a lower pressure than existing venturi to transfer the same amount of secondary fluid (air or other fluid) into the primary fluid (water or other fluid) resulting in a reduction of energy consumed to operate the unit.
As much as 60 to 80-percent of the costs of operating a municipal wastewater treatment plant is typically for energy used in the aeration of the treatment basins. A reduction in the cost of aeration of municipal wastewater treatment would have a significant impact on energy consumption in the United States and Worldwide. Other similar applications include lagoons, ponds, rivers, tanks, and other bodies of water treated for biodegradation of organic material and addition of oxygen for aquatic species or odor control. Generally, the use of venturi in water treatment is by pumping the water to increase its pressure and force it through the venturi to draw in air for oxygen to be supplied to microorganisms or other species that require dissolved oxygen to live in water or for odor control. The efficiency of the pumping process is another area where the present invention overcomes deficiencies of existing venturi designs. In addition to the specific design characteristics of a pump itself, the efficiency of a pump is greatly affected by its flowrate and differential pressure across the pump. In operation a venturi of any specific design is also affected by flowrate and differential pressure. According to Henry's Law, the ability to dissolve oxygen (from air or other source) is affected by total pressure at the point where the air comes in contact with the water. The total pressure supplied by a pump can be greatly increased by submerging the pump in water to make use of the head pressure of the water on the inlet side of the pump. The total pressure becomes the head pressure plus the differential pressure created by the pump.
The efficiency of a combined pump and venturi can be greatly improved by submerging the pump intake. However, it has been noted that the increase in head pressure of the water when the system is submerged creates a backpressure on the expanding discharge of the venturi and decreases the amount of air that can be drawn into the venturi. The greater the depth of operation, the larger the decreases in air suction. The present invention also overcomes this existing deficiency by adding a mixing chamber where the expanding outlet from the venturi can be made to rotate and reduce the backpressure commonly encountered when discharging directly into high-pressure water, such as in submerged operations.
In addition, the enclosed rotating discharge chamber mixes and holds the mixture (e.g. water-air) at the venturi outlet pressure to prevent the air from escaping and adding dissolved oxygen to the outlet stream (per Henry's Law) before it is discharged into the wastewater treating basin, such as in municipal wastewater treatment plants or treating ponds. The mixing chamber for rotating the output of venturi to reduce backpressure applies to one or any number of venturi that can be positioned around the circumference of the mixing chamber with a mixing chamber diameter and length selected for the flowrate of the specific application.
The cleaning of gases (also referred to as “purification of gases”) is a major function in the Oil and Gas Industry and in municipal wastewater collection and treatment systems as well as in many other industries. The gas purification function becomes even more difficult when the gases are hot, such as exhaust gases from internal combustion engines or other combustion functions, and need to be cooled and cleaned before being discharged in the atmosphere, in an environmentally sensitive area, or in an enclosed area. The ability to draw in hot gases in large quantities with venturi operating at low differential pressures could make certain exhaust gas cleaning functions practical.
In wastewater collection systems throughout municipalities the contaminated wastewater may be pumped to elevate the flowing wastewater to a certain level and then allow it to continue flowing downward toward the treatment plant in piping by gravity. In other instances the wastewater may be pumped and forced to flow under pressure (sometimes called a “forced main”) to its destination. In both the gravity flowing and forced main the microorganism action in digesting the organic contaminants may cause the oxygen to become depleted. The action is sometimes referred to as “causing the line or wastewater in the line to become septic.” When oxygen is depleted in collection lines the aerobic bacteria die and anaerobic bacteria become active. The action of the anaerobic bacteria generates methane and hydrogen sulfide gases that produce odors when released to the atmosphere. Treated water from municipal wastewater treatment plants and from large industrial plants are typically discharged to public streams, with some being piped under pressure some distance to a river or other stream before being discharged. Discharging a large amount of water into a river without sufficient dissolved oxygen to support life of fish, or other aquatic species, will cause the fish to die. The linear venturi of the present invention overcomes many deficiencies of existing venturi by reducing the differential pressures needed to operate and increasing efficiency of the venturi. The requirement for a pump can also be eliminated in many of this type of application by installing a venturi inside the pipe and causing a small differential pressure across the venturi to draw in atmospheric air from outside the pipe for aeration of the water flowing through the pipe. Typically, there are multiple pumps in lift stations of a municipal wastewater collection system. The pumps are turned on in sequence as the amount of wastewater to be transferred dictates. The linear venturi of the present invention can be used to aerate all wastewater in all collection lines. An inline venturi of the present invention requiring only a low differential pressure to operate can be installed at the outlet of each lift station pump. The additional energy consumed by a lift station pump for the increase in output pressure required (perhaps below 2-5 psi in most applications) to draw air into the line may typically be insignificant compared to installing additional pumps specifically for the venturi and operating them at pressures high enough to inject the output air-water mixture of the venturi downstream of the lift station pumps. As a pump is turned on air may be drawn into the line from within the well of the lift station. All water may be aerated as it continues to flow toward the treatment facility. Any hydrogen sulfide gas accumulated in the well may be drawn into the water, partially dissolved, and pumped downstream. In long lines the oxygen is likely to become depleted again in route to the treatment plant because of the activity of the bacteria. Additional linear venturi units can be positioned in the line at distances close enough to prevent oxygen depletion. With aeration in the lines the wastewater may be partially treated when it arrives at the treatment plant, reducing the treatment load on the plant in an economical way. In some systems the treatment load reduction could be significant. The amount of chemicals used for treating the wastewater to prevent hydrogen sulfide from coming out of solution in collection lines could be reduced, and in many cases possibly eliminated.
Water in a slow moving polluted river could be aerated at a relatively low cost with a linear venturi of the present invention by submerging a pump and venturi in the river water and operating them at a low differential pressure and using the head pressure of the river to contribute to the amount of oxygen that could be dissolved in the water within the venturi assembly before being released into the river. This could contribute to the food supply, to the health of the population, and to the economy by creating a fishing industry in many countries that cannot eat fish from their existing polluted rivers.
Vacuum is used for holding materials in machine tools, evacuating packages, holding containers in lifting operations, moving solids and liquids, evacuating dissolved gases in liquids, and countless other operations. While in most functions the vacuum is produced by vacuum pumps (the suction side of compressors) and blowers, the vacuum in many operations is produced by venturi. In this application the venturi apparatus may be referred to as a “vacuum generator.” The present invention overcomes deficiencies of existing venturi in this application by reducing the amount of primary fluid, such as air, and time needed to produce the vacuum. The result is an increase in efficiency.
Further, when pumping liquids having dissolved gases, cavitation can occur in the pump's impeller as the liquid is drawn into the pump. The low pressure produced by the suction of the pump causes the gases to come out of solution. The cavitation occupies space in the pump's impeller and typically reduces the amount of liquid that can be transferred. In many cases, the pump will not transfer any liquid and has to be shut down. An example of this problem that can have economic consequences includes the pumping of wastewater from a treating basin being aerated. Placing an eductor of the present invention at the outlet of the pump to draw the gases away from the impeller as the gasses come out of solution can increase the capacity of the pump and overcome deficiencies of existing pumps in such an application.
In the following discussions of the present invention the assembly of the venturi apparatus including a housing is referred to as an “eductor” with the “venturi” as the internal component with the reduced flow area by which the fluid velocity is increased and suction occurs. It will become clear to those skilled in the art having the benefit of this disclosure that the methods and apparatus in accordance with he present invention overcome, or at least minimize, the deficiencies of existing mixing apparatus and methods.